1. Field of the Invention
The present invention relates to a digital information recording carrier having digital information recorded in the form of a two-dimensional pattern on a recording surface of the carrier. The invention also relates to a digital information recording method and apparatus which can produce such digital information carriers. Further, the invention relates to a digital information decoding method and apparatus which can read and decode digital information recorded on such a digital information carrier.
2. Description of the Prior Art
FIG. 50 shows a two-dimensional data code which has been used in a method for recording digital information by arraying a matrix two-dimensionally on a recording surface (see U.S. Pat. No. 4,939,354). The two-dimensional data code is to record digital information by virtually setting matrix meshes corresponding to bits on a recording surface 220 of a recording carrier, and by assigning to each mesh a white or black color representing data.
In such a recording method, generally, control information representing the orientation of an information recording area 219 and the size of a cell (data density) is provided for reading convenience's sake. In the example of FIG. 50, as the control information, the perimeter of the rectangular information recording area 219 is provided with a linear portion 212 on its two adjoining sides 221 and a clocking information portion 216 on the remaining two sides 231. The linear portion 212 is formed of adjoining black cells, and the clocking information portion 216 is formed of alternately connected white and black cells. During a reading operation, the orientation of the information recording area 219 is detected due to the linear portion 212, and the size of cells is detected through the clocking information portion 216.
In the above conventional digital information recording method, however, the clocking information portion 216 will be farther away from the data as the size of the information recording area 219 increases. This is because the clocking information portion 216 is provided along the perimeter of the information recording area 219. As a result, due to factors such as distortion of the recording surface 220, characteristics of the reading device (scanner, CCD camera, etc.), or the like, a large difference in data position between recording and reading operations will be caused in the vicinity of the center of the information recording area 219, resulting in reading errors. For example, instead of originally intended information on a cell of the fifth row, the fourth column, the information on the cell of the sixth row, the fifth column may be erroneously read. Consequently, the conventional digital information recording method has a problem that the size of the information recording area 219 cannot be increased and therefore that the storage capacity cannot be increased.